Centering a pop-up window in Javascript

I come across this a lot, but always seem to forget some little detail... so I'm putting it here as a reference:

function wopen(url, name, w, h)
{
// Fudge factors for window decoration space.
// In my tests these work well on all platforms & browsers.
w += 32;
h += 96;
wleft = (screen.width - w) / 2;
wtop = (screen.height - h) / 2;
// IE5 and other old browsers might allow a window that is
// partially offscreen or wider than the screen. Fix that.
// (Newer browsers fix this for us, but let's be thorough.)
if (wleft < 0) {
w = screen.width;
wleft = 0;
}
if (wtop < 0) {
h = screen.height;
wtop = 0;
}
var win = window.open(url,
name,
'width=' + w + ', height=' + h + ', ' +
'left=' + wleft + ', top=' + wtop + ', ' +
'location=no, menubar=no, ' +
'status=no, toolbar=no, scrollbars=no, resizable=no');
// Just in case width and height are ignored
win.resizeTo(w, h);
// Just in case left and top are ignored
win.moveTo(wleft, wtop);
win.focus();
}